There are few infrared sources capable of obtaining strong intensity at a specific wavelength in an infrared wavelength range.
Although some of expensive lasers are oscillated at the specific wavelengths, the specific wavelengths cannot be set to arbitrary values.
There is considered a device in which light with arbitrary wavelengths is taken out from radiant light radiated from a heater, etc. using a filter, or the like. However, such a device has problems that the number of components is large, a method of manufacturing a wavelength filter is complicated, and output energy is extremely low.
Also, there has been proposed a high-temperature light emitting micro cavity light source (for example, see Japanese Patent Application National Publication No. 2001-519079). However, the high-temperature light emitting micro cavity light source has a complicated structure.
On the other hand, an application for light sources with an infrared wavelength range has been expanded to fields including medical care and biotechnology.
There is a non-dispersive infrared absorption method as a method of analyzing gas or liquid, utilizing absorption of infrared rays radiated from materials. The non-dispersive infrared absorption method is a method that uses infrared absorption lines inherent in materials to measure concentration of the corresponding materials or composition of the materials. As analysis systems using a non-dispersive infrared absorption method, there are systems in various forms such as a stationary type system built in production equipment or devices and a portable system driven by a battery.
FIG. 61 is a view showing a basic configuration of the analysis system using the non-dispersive infrared absorption method. The analysis system includes an infrared source 301, a measuring cell 207, a means 211 that periodically changes intensity, a wavelength selecting element 303, an infrared sensor 203, and a demodulation means 205. As the infrared source 301, a white infrared source (lamp) using black body radiation is exclusively used. As the means 211 that periodically changes intensity, there is used a chopper that periodically interrupts infrared rays by rotating a shutter covering the light source or a radial slit. As the wavelength selecting element 303, a narrow range filter transmitting a specific wavelength alone using a dielectric multi-layer film or the like is used. As the infrared sensor 203, various detectors such as a pyroelectric element, a bolometer, a thermopile, a heat flux sensor and the like are used. Infrared rays from the infrared source 301 pass through the measuring cell 207 including an object to be measured and arrive on the means 211 that periodically changes intensity, the wavelength selecting element 203, and the infrared sensor 203, in succession.
FIG. 62 is a view showing relations among absorbance of the object to be measured (for example, gas), intensity of lights, transmittance of the wavelength selecting element. FIG. 62(a) is a view showing absorbance of gas A to be measured with respect to wavelength. It shows that the absorbance of gas A to be measured is large at a wavelength λS. FIG. 62(b) shows intensity of infrared rays radiated from the infrared source 301 with respect to wavelength. The infrared source 301 radiates infrared rays with intensity distribution corresponding to temperature over a wide wavelength range according to a Planck's law. FIG. 62(c) shows transmittance of the wavelength selecting element 303 with respect to wavelength. The wavelength selecting element 303 is a narrow range filter transmitting lights with a narrow wavelength range around λS alone.
Transmittance of infrared rays with wavelength λS is changed according to a concentration of the gas to be measured in the measurement cell, and therefore an output of the infrared sensor 203 is also changed. The concentration of the gas is calculated from a comparison between a detected signal and a reference signal previously obtained, based on Lambert' law. λS is not always set to the peak wavelength at which absorption becomes maximized, but is determined in consideration of various factors such as that of avoiding overlaps with absorption of other coexisting gases.
Actually, since this method is hard to obtain reliable results due to an influence of aging change, etc. of the elements or the optical system, in many cases some kind of reference signals are used.
FIG. 63 shows an analysis system using a reference sample. Gas B with previously known composition is sealed in a reference cell 207A, and a wavelength selecting element 3031A and an infrared sensor 203A are installed for measuring concentration of gas B. Gas A to be measured is sealed in a measurement cell 207B, and a wavelength selecting element 3031B and an infrared sensor 203B are installed for measuring a concentration of gas A. A concentration of gas A is obtained from a ratio between a signal of the infrared sensor 203A and that of the infrared sensor 203B and from absorbance at λS of object gas A to be measured and that of object gas B to be measured. In many cases, the reference cell 207A is sealed with the same kind of gas as the gas to be measured.
FIG. 64 is a view showing the analysis system in a two-wavelength method. A wavelength selecting element 3033 and the infrared sensor 203A are installed for infrared rays at wavelength λS at which absorbance of the gas to be measured is to be large, and a wavelength selecting element 3035 and an infrared sensor 203B are installed for infrared rays at wavelength λR at which absorbance is to be small. Transmittance of the wavelength selecting element 3033 at wavelength λS is the same as characteristics of the wavelength selecting element 303 shown in FIG. 62(c). Transmittance of the wavelength selecting element 3035 at wavelength λR is shown in FIG. 62(d). A concentration of gas A is obtained from a ratio between a signal of the infrared sensor 203A and that of the infrared sensor 203B and from absorbance at wavelength λS and that at wavelength λR of object gas A to be measured.
The analysis system as described above uses infrared rays with the specific wavelengths determined according to materials to be measured. On the other hand, as shown in FIG. 62(b), infrared sources in conventional analysis systems radiate infrared rays with a wide wavelength range. Thus, in conventional analysis systems, only infrared rays with wavelengths selected by a wavelength selecting element, such as a filter, among the infrared rays radiated from the infrared source, are used and infrared rays with other wavelengths are discarded. Therefore, conventional analysis systems waste much energy and cannot reduce an output from the infrared source, and therefore it is difficult to make the infrared source compact. As a result, conventional analysis systems are low in energy efficiency and are relatively large in size.
In order to monitor an object to be measured, a monitor system (for example, see Japanese Patent Application Laid-Open No. 2005-106523) in which a light source radiates lights with a specific wavelength and a sensor receives the lights, is used.
In many cases, such systems use a silicon sensor as a light receiving element. Since silicon sensors have high sensitivity in a range from 400 nm to 1000 nm, the systems use lights with a wavelength within the range in many cases. However, sunlight and illumination light have much wavelength component in the range, which becomes noise component and causes the systems to malfunction. In order to avoid an influence of noise such as sunlight, it is advantageous to use lights with a infrared wavelength range.
As described above, an infrared source radiating lights with an infrared wavelength range is required for a system monitoring an object. However, there are few infrared sources radiating lights with strong intensity at specific wavelengths in an infrared wavelength range.
Lasers oscillated at specific wavelengths are expensive and the specific wavelengths cannot be set to arbitrary values.
A device in which lights with arbitrary wavelengths are taken out from lights radiated from a heater, etc. using a filter, or the like, is available. However, such a device has problems that the number of components is large, a method of manufacturing a wavelength filter is complicated, and output energy is extremely low.
Further, a high-temperature light emitting micro cavity light source (for example, see Japanese Patent Application National Publication No. 2001-519079) has been proposed. However, the structure is complicated.